This invention relates to the field of assisting persons afflicted with partial paralysis. Such partial paralysis may be the result of a stroke or mild spinal cord injury. In either event, such persons customarily are able to move their limbs but only ineffectively and at reduced contraction levels.
In recent years there has been a great deal of activity directed toward restoring useful movement to totally paralyzed limbs. Such effort has produced computer controlled stimulation systems for producing leg exercise as disclosed in Petrofsky et al. U.S. Pat. No. 4,480,830 and in Petrofsky et al. U.S. Pat. No. 4,499,900. Computer controlled arm movement has also been developed as disclosed in Petrofsky U.S. Pat. No. 4,558,704.
During muscular contraction by non-handicapped persons the brain generates electromyographic signals which are transmitted by the spinal cord to motor control points for the muscles which are to contract. In many cases of total paralysis there is a break in the communication link between the brain and the motor control point, but the muscle itself is otherwise undamaged. In such cases it has been found possible to generate stimulation signals which are artificial substitutes for the natural electromyographic signals. The stimulation signals are applied to the muscles through transcutaneous electrodes. It is also possible to achieve muscle stimulation through surgically buried electrodes.
In the case of partial paralysis there is no need to create an artificial substitute for the natural electromyographic signals. The signals are not interrupted but are merely degraded. It is therefore desirable to utilize such electromyographic signals for controlling functional electrical stimulation.
Prior art devices have used electromyographic signals in a variety of applications. For example, apparatus as disclosed in Tanie et al. U.S. Pat. No. 4,314,379 senses electromyographic signals for controlling a servo device connected to operate an artificial arm. A system has also been proposed for measuring electromyographic signals on a paralyzed person's upper body and using those signals for controlling stimulation of the lower extremities. See Graupe et al. "Electromyographic Control of Functional Electrical Stimulation in Selected Patients", Orthopedics, July 1984, pp. 1134-1138. Both of these prior art approaches sense electromyographic signals at one location and control activity at a different location.
Another system as disclosed in Vincent et al. U.S. Pat. No. 3,628,538 measures electromyographic signals at a motor control point and uses the measurement for control of stimulation signals applied at the same point. The system is used for stimulating bladder control muscles. Accordingly, it utilizes electrical circuitry which listens to electromyographic signals for a period of about 50 milliseconds and then stimulates the bladder control muscles for a period of about 10 seconds. Such a system is not suitable for smooth continuous control of arm or leg activity.